Pyrolysis process and apparatus for manufacture of ketenes and anhydrides



P 6 E. 5. PA! ER ETAL 3,403,181 PYROLYSIS PROCESS AND PARATUS, FORMANUFACTURE OF'KETENES AND, ANl-IYDRIDES Original Filed May 4, 1964 Y 3Sheets-Sheet l v I pHAMBER v4 J KErE/VE our r0 CONDENSER Vanna 4 sracx';

3 bow/1v s. INT/5R .ROBERT ETREY JOHN -/-/L JENSEN. JR. INVENTQRSATTORNEYS Sept. 24, 1968 E. s. PAINTER ET AL 3,403,181

PYROLYSIS PROCESS AND APPARATUS FOR MANUFACTURE OF KETENES ANDANHYDRIDES Original Filed May 4, 1964 3 Sheets-Sheet 2 PREHEA rSUPERHE/J 7" cRA GK/NG A CR4 CK/A/G CHAMBER CHAMBER CHA MBER CHAMBERSTREAM- A 78 7 A DRAFT DRAFT .58 \56 54 RA scRuBBER as //6 62 v 92 '//0CONDENSER I08 VAPOR PREssuRE :2: Q1 MEASURING pEv/cE K AIR OPERATED vVALVE FoR HOAC FEED CRUDE PRODUCT 4| IP OVERFLOW HEAT ExcH /vaER cooLEREDW/NS. PAINTER ROBERT c. PETRE) 7 JOHN H. JENSEN JR- INVENTORSArmR/vEYs Sept. 24, 1968 E. s. PAINTER ET AL 3,403,181

PYROLYSIS PROCESS AND APPARATUS FOR MANUFACTURE OF KETENES ANDANHYDRIDES Original Filed May 4, 1964 3 Sheets-Sheet 5 EDWIN 5. PAINTERROBERT C. PETRE) JOHN H. JENSEN JR.

INVENTORS By QMM ATTORNEYS United States Patent 3,403,181 PYROLYSISPROCESS AND APPARATUS FOR MANUFACTURE OF KETEN ES AND ANHYDRIDES EdwinS. Painter, Robert C. Petrey, and John H. Jensen, Jr., Kingsport, Tenn.,assignors to Eastman Kodak Company, Rochester, N.Y., a corporation ofNew Jersey Continuation of application Ser. No. 364,509, May 4, 1964,which is a continuation-in-part of application Ser. No. 31,441, May 24,1960, now Patent No. 3,136,811, dated June 9, 1964. This applicationJuly 20, 1966, Ser. No. 566,712 The portion of the term of the patentsubsequent to July 5, 1983, has been disclaimed 5 Claims. (Cl. 260-5855)ABSTRACT OF THE DISCLOSURE A system for preparing ketenes by pyrolysisof material in a furnace having interwound helical coils in itspreheating and superheating chambers, with means for subsequentconversion to anhydride.

This application is a continuation of Ser. No. 364,509, filed May 4,1964, now abandoned, which in turn is a continuation-in-part of Ser. No.31,441, filed May 24, 1960, now U.S. Patent 3,136,811, issued June 9,1964.

This invention relates to the manufacture of ketenes and anhydrides.More particularly, this invention concerns the manufacture of ketenes bythe pyrolysis of acetic acid and the conversion of the ketene to aceticanhydride.

Our co-workers have disclosed various methods and apparatus for themanufacture of ketenes and anhydrides by pyrolysis of certain compoundssuch as acids, ketones, and other ketenizable materials. In U.S. Patents2,258,985 and 2,393,778 they have described one and two-chamber furnacesand processes for pyrolysis of ketenizable organic compounds. In US.Patent 2,541,471 our co-workers have described a three-chamber furnace.Painter, one of the inventors herein, in U.S. 2,784,065 has disclosedanother embodiment of a three-chamber furnace. Painter et al. in US.2,776,192 have disclosed that superheating may be carried out onseparate streams of the material to be ketenized. In Ser. No. 31,441, ofwhich the instant application is a continuation-in-part and in whichapplication claims have been allowed, we have described a fourchamberprocess and apparatus. According to said Ser. No. 31,441 separatestreams of ketenizable material are preheated in different parts of thesame preheating chamber, and then superheated in different parts of thesame superheating chamber before being cracked in separate crackingchambers.

While all of the foregoing procedures of Painter and co-Workers haveproved highly successful in the manufacture of ketenes, a new processand apparatus by which an equally good conversion to ketene and an aseflicient way of producing ketene may be achieved represents a highlydesirable result. After extended investigation, we have found a processand apparatus whereby as great or greater efiiciency of production thanheretofore known in the production of ketenes and correspondinganhydrides is provided.

This invention has for one object to provide apparatus and process ofimproved economy for manufacture of ketenes. A particular object is toprovide an improved procedure for pyrolysis of acetic acid to ketene.Another object is to provide an economical manner of converting keteneto acetic anhydride whereby improved economy of construction, yield, andconversion may be secured. A special object is to provide an apparatusarrangement whereby ease of preparation of ketene may be increased.Still another object is to provide a novel apparatus arrangement andmethod for producing ketenes and anhydrides which permit an alternateconstruction capable of equal or more efiicient results. Another objectis to provide an apparatus of the class indicated wherein there isprovided a special coil arrangement. Other objects will appearhereinafter.

In the broader aspects of our invention we have found that in afour-chamber furnace made up of two cracking chambers in parallelconnected in series with preheating and superheating chambers when twoparallel interwound coils are used in both preheating and superheatingcham bers we are able to use efiiciently substantially all of theheating gas with a minimum amount of waste heat. By such an arrangementwe are also able to control the temperature from top to bottom of eachchamber without undue variation. In further detail, two separate streamsof material to be cracked enter the top of the preheating chamber andwind around in parallel paths in a helicalshaped coil arrangement untilthey reach the bottom of the chamber. Then each separate stream ispreferably carried upward along the vertical axis of the core formed bythe coils and then conducted through the superheating chamber in asimilar manner. One stream then passes through a single coil in one ofthe cracking chambers and the other stream passes through a similar coilin the other cracking chamber before the two streams join as one for thecontacting of the ketene with acetic acid to produce acetic anhydride.The coil arrangements in the two parallel cracking chambers which havethe separate streams of ketenizable material introduced from thepreheating and superheating chambers are of similar construction to thepreheating and superheating chambers with the principal exception thatthere is only one coil in each rather than two parallel coils in each.

We have also found by one embodiment of our invention that we maycontrol the composition of the anhydride-acid process stream forefiiciency in converting ketene to anhydride by withdrawing samplestreams of the ketene-acetic acid reaction product and using adilferential vapor pressure transmitter to.compare the vapor pressure ofthe acetic anhydride process stream to the vapor pressure of a standardsolution such as methyl Cellosolve. The measure of the differencebetween the two is transmitted to a control station which operates apneumatic valve on the acid feed and controls the amount of acidintroduced to the anhydride unit.

A further understanding of our invention may be had from a considerationof the attached drawing forming a part of the present application.

FIG. 1 is a semidiagrammatic side elevation view in section illustratinga four-chamber furnace embodying the coil arrangement of the presentinvention. As will be apparent hereinafter, since many of the details ofconstruction may be the same as presently used construction for suchtype of furnaces, extended description of FIG. 1 will not be necessary.

FIG. 2 is a more fully diagrammatic side elevation view in aparticularly simplified form for illustrating the piping and coilarrangement in a four-chamber furnace of the present invention. Thisfigure has been presented in particular to illustrate the basicinventive features of the instant invention.

FIG. 3 is a semidiagrammatic side elevation view of an anhydride formingunit such as may be used in conjunction with the furnaces of the presentinvention. That is, the ketene produced in the furnaces of the presentinvention may be utilized in the process and apparatus of FIG. 3 for theproduction of a uniform anhydride product.

FIG. 4 is an exploded view of coils 74 and 76 of the preheat chamber ofFIG. 2 with coils pulled apart somewhat to show their parallel windingconstruction in somewhat more detail. These coils are similar inconstruction to coils 82 and 70 of the superheat chamber.

Referring now to FIG. 1, it can be noted that many of the parts shown inthis figure may be the same or similar to the parts described inabovementioned companion Patents 2,541,471; 2,784,065 and 2,776,192 andco-pending US. patent application Ser. No. 31,441 and that the materialsof construction may be the same as described in these patents and inthis co-pending application. The furnace is comprised of a furnacehousing which would be of suitable ceramic or brick work for enclosingthe coils for preventing heat escape and also for bringing the heatingmedium in close contact with the coils. The interior of this furnacehousing is divided. into four chambers 12, 14, 16 and 18. Each of thesechambers is separated from the other chambers by suitable baffle walls20, 22, 24 and 26. These ceramic bafile walls may be of any desiredconstruction such as the various constructions disclosed in the patentsand co-pending application just referred to. Chamber 18 is provided withan exit 28 whereby the heating gases may be exhausted to a stack (notshown).

In the construction shown in FIG. 1, the combustion chamber 30 isprovided with one or more burners 32. However, supplemental to or inlieu of the combustion chamber, individual burners may be inserted intoeach of the chambers 12, 14, 16, etc. In such arrangement the burnersare preferably positioned to discharge tangentially to the Walls and notto impinge directly on the coils in the chamber. Similar remarks applyto burner 34 in that it would be angled so as not to impinge directly onthe parallel-aligned coils 36 and 38.

In addition to the refractory bafiies and the like just referred to, inat least chambers 12 and 14, and if desired, in the other chambers,there would be provided refractory core members such as 40 and 42 whichcore members are encircled by the cracking coils to be described in moredetail hereinafter. Extended description of these core members, whichmay be solid or tubular, is unnecessary inasmuch as the constructionthereof may be substantially exactly in accordance with the disclosurein companion US. Patent 2,541,471.

In each of these chambers of the four-chamber furnace there arepositioned coils and piping through which is fed the ketenizablematerial to be cracked or pyrolyzed to the ketene. That is, crackingcoils 44 and 46 are positioned in chambers 12 and 14. superheating andpreheating coils 48, 50, 36 and 38 are positioned in the other twochambers 16 and 18. A further understanding of this coil arrangement andpositioning, which is an important part of the present invention, willbe had from a consideration of FIG. 2 which will now be described.

In this schematic and simplified view of FIG. 2, it will be observedthat there has been provided the areas 52, 54, 56 and 58 correspondingto the four chambers referred to above. Such areas or chambers have beenfurther identified by the legends appearing on FIG. 2 as crackingchamber, superheating chamber and preheating chamber.

In connection with the cracking chamber it will be noted that inaddition there has been designated the capital letters A and Bcorresponding to stream A and stream B noted on the left of FIG. 2. Inthe arrangement of the present invention the piping and coilconstruction is such that two streams, namely A and B of the ketenizablematerial may be fed through the four chamber furnace simultaneously, thetwo streams joining at point 60 to leave the furnace through the singleconduit 62.

Chambers 52 and 54 each contain a cracking coil 64 and 66 piped inparallel.

Considering cracking coil 64, this is connected by conduit 68 to thesuperheat coil 70, which superheat coil is connected by conduit 72 tothe preheat coil 74. This preheat coil leads alongside parallel coil 76in a spiral course back through conduit 78 to the feed (stream A) of theketenizable material.

In a similar manner, cracking coil 66 is connected by a conduit 80 to asuperheating coil 82. It will be noted that this superheating coil 82 ispositioned so as to follow a course parallel to the spiral course ofcoil 70 of line A. Such an arrangement is thought to provide optimumheat distribution.

Continuing further with the piping of stream B, it will be observed thatthe superheat coil 82 is connected by conduit 84 to the preheat coil 76which coil leads into the feed of stream B through conduit '86.

From this simplified piping diagram it will be observed that two streamsA and B of ketenizable material may be fed into the four-chamber furnaceof the present invention so as to follow each other in a substantiallyparallel course in both preheating and superheating chambers beforeseparating for each to pass through its own cracking chamber. In eachinstance each stream A and B is subjected to approximately comparablepreheating and superheating treatment in the chambers 58 and 56. Theneach of the streams A and B enters its separate cracking chamber 52 and54 wherein the final pyrolysis takes place. The resultant pyrolysisproducts are united at point 60 to the single conduit 62 through whichthe pyrolysis products are conducted to a condenser and other treatmentsto separate and/or utilize the products.

We have discovered that the capacity of the furnaces of the class underdescription is limited both by pressure drop in the tubing and by heatinput to the furnace. We have found that the new arrangement of thepresent invention providing parallel sets of preheating and superheatingcoils otherwise in accordance with the arrangement of FIG. 2 contributesto a reduced pressure drop for a given flow rate and an increase infeed. Expressed in another way, by the new piping arrangement of thepresent invention the pressure drop obtained is equivalent to orsuperior to the pressure drop obtained in prior art three coil furnacesand the four-coil furnaces shown in copending US. patent applicationSer. No. 31,441.

Referring now to FIG. 3, we have disclosed process and apparatus bywhich the ketene produced by the present invention may be utilized. Theketene leaving the furnace through conduit 62 may be passed into acondenser 88, the condensables are withdrawn at 90. The ketene gas thuspreliminarily treated passes through conduit 92 into scrubber 94. Inthis scrubber the ketene gas is contacted with a circulating stream of amixture of acetic anhydride and acetic acid entering the scrubberthrough conduit 96.

Acetic acid is admitted to this scrubber system through the supply line98 which supply line contains therein automatic valve 100. The reactionproduct of the ketene with the acetic acid Withdrawn from the bottom ofthe scrubber at point 102 is pumped by pump 104 through heat exchanger106 and then through the orifice device 108. This device is associatedwith the control system 110 which is interconnected with valveaforementioned. The reaction product overflows from scrubber 94 throughconduit 112.

The control device functions to measure automatically the differencebetween vapor pressure of the flowing stream which is by-passed throughlines 114 and 116 and a control solution (not shown). Such measurementsare based on the vapor pressure and the operation of valve 100 inresponse thereto permits the automatic control of the reaction productof the ketene with the acetic acid to an accuracy within :0.5%. Thispermits the utilization of the ketene for making an acetic anhydride oflimited variation.

A still further understanding of our invention will be had from aconsideration of the following examples which are set forth toillustrate certain of our preferred embodiments of operations.

Example I A furnace with the arrangement of coils of FIG. 2 was used foran interval of several weeks in the production of 115,000 pounds per dayof acetic anhydride. The coil arrangement used resulted in reduction ofthe pressure drop through the furnace and thereby produced a bettervacuum, thus accounting for increased efliciency of operation. We havealso found it possible to use this coil arrangement in three-chamberfurnaces such as those of aforesaid U.S. Patents 2,541,471; 2,784,065and 2,776,- 192.

Example II The control arrangement shown in FIG. 3 was used to controlthe percent acid in the scrubber process of converting ketene toanhydride as shown above to an accuracy of :0.5% acid. Normal operatortemperature rise analysis had a standard deviation of :0.85%.

To supply additional heat auxiliary gas-fired burners may be used in thefirst chamber, now known as the preheat or preheating chamber. The useof burners in such chamber increases the temperature of the flue gasleaving the furnace. As already indicated above, when burners areinserted in the chambers, they are preferably positioned so the flamewill not impinge directly on the coils. The fuel gas usage according toour invention amounts to about 2.25 to 2.5 cu. ft. per lb. of anhydride.

According to our invention and further detail as may :be noted byreference to FIG. 2 stream A and stream B flow in parallel through thepreheat chamber, superheat or superheating chamber and then stream Agoes to the fourth chamber designated the A cracking chamber and streamB goes to the third chamber designated B cracking chamber. Stream A andstream B follow parallel coiled paths in both preheat and superheatchambers.

The hot combustion gases from the A cracking chamber leave this chamberat the bottom and enter the B cracking chamber at the bottom and leaveat the top thereof. The waste gases leave the superheat chamber at thebottom and enter the preheat chamber. The preheat chamber coils have ashell inside the coil. The hot gases entering at the bottom of thepreheat chamber travel upward around the coils and outside the shell andenter the shell at the top of the chamber and travel down past the draftdamper on to the steam generator and the waste gas stack. Gas burnersmay be fired in the annular space around the coil in the preheat chambersupplying additional heat.

For feeds A and B we used glacial acetic acid of approximately 99.95%purity. The acetic acid, as it entered the perheat chamber of FIG. 2,had injected therein a small amount of catalyst. That is, there wasincorporated in the acetic acid feed a small amount of phosphatecatalyst. Suitable catalysts are trimethyl phosphate, tri-isopropylphosphate and tripropyl phosphate and other phosphate esters of thistype. Streams A and B which are in series in the preheat and superheatchambers were subject to a temperature in the preheat chamber within therange of 600-1000 C. In the superheat chamber the temperature range waswithin the range of 750l500 C.

In the cracking chambers where the coils are in parallel arrangement,the temperature was within the range of 750l500 C. The heat was suppliedby several burners positioned in all the chambers as needed to supplysufficient heat by burning natural gas to maintain the temperaturesspecified aforesaid in the respective chambers.

The pressure drop with the piping and coil arrangement of the presentinvention, from the point of entry :before the feed of the preheat zoneto the exit at conduit 62 was of the order of 240 mm. As may be noted,such pressure drop is relatively low and compares favorably with thepressure drop of two and three and other fourchamber furnaces.

The rate of feed of the glacial acetic acid to the process in eachseparate line in accordance with Example I was of the order of 2700 lbs.per hour. The conversion of such feed to ketene was of the order of-85%.

The ketene produced in accordance with Example I was reacted with aceticacid in an apparatus as diagrammatically disclosed in FIG. 3 to give ahigh quality uniform acetic anhydride. As described above in connectionwith FIG. 3, the reaction of the ketene and acetic acid is controlled bycontinuously withdrawing a sample stream of the reaction product andmeasuring the vapor pressure by means of a differential vapor pressuretransmitter and controlling the acetic acid flow by means of acontroller obtainable commercially from Foxboro and other companies. Bysuch controlled reaction wherein the feed of the acetic acid reactedwith the ketene is controlled by the vapor pressure of the reactionproduct, there was obtained a very uniform acetic anhydride.

Although the process has been described primarily with respect to theconversion of acetic acid to ketene, this being one of the principaltypes of conversions carried out commercially, our process and apparatusmay be utilized in the pyrolysis of other ketenizable materialsexemplified by acetone, ethyl acetate, propionic acid and oher ketonesand acids of this type.

It is thought apparent from the foregoing that we have provided a newand improved piping and coil arrangement which is specially adapted forfour-chamber furnaces for the production of ketenes and anhydrideswhereby increased economy is made possible with equal or better yieldsthan heretofore possible. Also, we have shown how to control theuniformity of the acetic anhydride produced from ketene resulting frompyrolysis of acetic acid.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it 'will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention as described hereinabove and as defined in the appendedclaims.

We claim:

1. A pyrolysis process using preheating, superheating, and separatepyrolysis zones, said process comprising the steps of:

(1) preheating two streams of material to be pyrolyzed by passing saidstreams through interwound helical paths in said preheating zone,

(2) superheating the preheated streams by passing them respectivelythrough interwound helical paths in said superheating zone, and

(3) pyrolyzing said superheated streams by passing them respectivelythrough helical paths in separate pyrolysis zones.

2. The invention of claim 1 wherein said preheated streams are treatedin helical paths of substantially the same length, said superheatedstreams are treated in helical paths of substantially the same length,and wherein said material is ketenizable and said pyrolysis processproduces ketenes.

3. An apparatus for pyrolyzing a stream of material comprising, incombination:

(1) a furnace housing;

(2) a first pair of interwound helical coils of tubing arranged in apreheat chamber defined by said housmg;

(3) a second pair of interwound helical coils of tubing arranged in asuperheat chamber defined by said housing;

(4) two separate helical coils of tubing arranged in separate pyrolysischambers defined by said housing;

(5) first conduit means for serially connecting one coil of said firstpair to one coil of said second pair, and connecting the other coils ofsaid first and second pair;

(6) second conduit means for serially connecting one coil of said secondpair to one of said separate coils, and connecting the other coil ofsaid second pair to the other separate coil; and

(7) said coils of tubing and said first and second conduit meansproviding a flow path for sal'i'i stream of material.

4. The invention of claim 3 wherein said first and second pair of coilsextend from substantially the top to the bottom of their respectivechambers.

5. The invention of claim 4 wherein said first conduit means extendsfrom the bottom of said first pair of coils,

through the core formed by said first pair of coils, and to the top ofsaid second pair of coils.

References Cited UNITED STATES PATENTS 2,776,192 1/1957 Painter et a1.23277 2,784,065 3/1957 Painter 23--277 2,541,471 2/1951 Hull et a1.23-277 2,967,515 1/1961 Hofstede et al. 165-145 X 3,259,469 7/1966Painter et a1. 63 277 JOSEPH SCOVRONEK, Primary Examiner.

